In recent years, traditional Japanese koji-fermented food products using koji have been re-evaluated and become popular. “Koji” means a product obtained by steaming rice, wheat, bean or the like, and then allowing koji mold to proliferate therein. Among them, koji obtained by allowing koji mold to proliferate in rice is referred to as “rice koji (malted rice)”. The malted rice is mainly used in the production of fermented food products such as sake (rice wine), soy sauce, miso (fermented bean paste), or amazake (sweet fermented rice drink). In addition, the malted rice is also used as a seasoning. Koji mold contained in this malted rice has an ability to produce many types of enzymes such as protease or amylase. Accordingly, such malted rice is added to or sprinkled on a food material such as meat, fish or vegetables to degrade ingredients contained in the food material, so that the food material itself can be softened, or a natural sweet taste or umami (good taste) can be given to the food material. As such koji mold used for the malted rice, yellow koji mold such as Aspergillus oryzae has been mostly used, as described in Patent Literature 1.
On the other hand, black koji mold is another koji mold. As in the case of other koji molds, the black koji mold is characterized in that it produces many types of enzymes such as protease or amylase. However, the black koji mold is characterized in that it produces a large amount of citric acid. The black koji mold is mainly used in the production of distilled spirits such as Awamori. Accordingly, regarding the black koji mold, studies have been mainly conducted, focusing on the enhancement of the enzyme activity of amylase to glycosylate starch contained in raw materials so as to improve the efficiency of production of distilled spirits, as described in Patent Literature 2.